Search

The system B2O3-Al2O3-SiO2 (BAS) includes two ternary phases occurring naturally, boromullite, Al9BSi2O19, and boralsilite, Al16B6Si2O37, as well as synthetic compounds structurally related to mullite. The new mineral vránaite, a third naturally occurring anhydrous ternary BAS phase, is found with albite and K-feldspar as a breakdown product of spodumene in the elbaite-subtype Manjaka granitic pegmatite, Sahatany Valley, Madagascar. Boralsilite also occurs in this association, although separately from vránaite; both minerals form rare aggregates of subparallel prisms up to 100 µm long. Optically, vránaite is biaxial (-), nα = 1.607(1), nβ = 1.634(1), nγ = 1.637(1) (white light), 2Vx(calc) = 36.4°, X ≈ c; Y ≈ a; Z = b. An averaged analysis by EMP and LA-ICP-MS (Li, Be) gives (wt%) SiO2 20.24, B2O3 11.73, Al2O3 64.77, BeO 1.03, MnO 0.01, FeO 0.13, Li2O 1.40, Sum 99.31. Raman spectroscopy in the 3000-4000 cm-1 region rules out the presence of significant OH or H2O. Vránaite is monoclinic, space group I2/m, a = 10.3832(12), b = 5.6682(7), c = 10.8228(12) Å, β = 90.106(11)°; V = 636.97(13) ų, Z = 1. In the structure [R1 = 0.0416 for 550 Fo > 4σFo], chains of AlO6 octahedra run parallel to [010] and are cross-linked by Si2O7 disilicate groups, BO3 triangles, and clusters of AlO4 and two AlO5 polyhedra. Two Al positions with fivefold coordination, Al4 and Al5, are too close to one another to be occupied simultaneously; their refined site-occupancy factors are 54% and 20% occupancy, respectively. Al5 is fivefold-coordinated Al when the Al9 site and both O9 sites are occupied, a situation giving a reasonable structure model as it explains why occupancies of the Al5 and O9 sites are almost equal. Bond valence calculations for the Al4 site suggest Li is likely to be sited here, whereas Be is most probably at the Al5 site. One of the nine O sites is only 20% occupied; this O9 site completes the coordination of the Al5 site and is located at the fourth corner of what could be a partially occupied BO4 tetrahedron, in which case the B site is shifted out of the plane of the BO3 triangle. However, this shift remains an inference as we have no evidence for a split position of the B atom. If all sites were filled (Al4 and Al5 to 50%), the formula becomes Al16B4Si4O38, close to Li1.08Be0.47Fe0.02Al14.65B3.89Si3.88O36.62 calculated from the analyses assuming cations sum to 24. The compatibility index based on the Gladstone-Dale relationship is 0.001 ("superior"). Assemblages with vránaite and boralsilite are inferred to represent initial reaction products of a residual liquid rich in Li, Be, Na, K, and B during a pressure and chemical quench, but at low H2O activities due to early melt contamination by carbonate in the host rocks. The two BAS phases are interpreted to have crystallized metastably in lieu of dumortierite in accordance with Ostwald Step Rule, possibly first as "boron mullite," then as monoclinic phases. The presence of such metastable phases is suggestive that pegmatites crystallize, at least partially, by disequilibrium processes, with significant undercooling, and at high viscosities, which limit diffusion rates. [ABSTRACT FROM AUTHOR]

Oxy-schorl (IMA 2011-011), ideally Na(Fe2+2Al)Al6Si6O18(BO3)3(OH)3O, a new mineral species of the tourmaline supergroup, is described. In Zlatá Idka, Slovak Republic (type locality), fan-shaped aggregates of greenish black acicular crystals ranging up to 2 cm in size, forming aggregates up to 3.5 cm thick were found in extensively metasomatically altered metarhyolite pyroclastics with Qtz+Ab+Ms. In Přibyslavice, Czech Republic (co-type locality), abundant brownish black subhedral, columnar crystals of oxy-schorl, up to 1 cm in size, arranged in thin layers, or irregular clusters up to 5 cm in diameter, occur in a foliated muscovite-tourmaline orthogneiss associated with Kfs+Ab+Qtz+Ms+Bt+Grt. Oxy-schorl from both localities has a Mohs hardness of 7 with no observable cleavage and parting. The measured and calculated densities are 3.17(2) and 3.208 g/cm3 (Zlatá Idka) and 3.19(1) and 3.198 g/cm3 (Přibyslavice), respectively. In plane-polarized light, oxy-schorl is pleochroic; O = green to bluish-green, E = pale yellowish to nearly colorless (Zlatá Idka) and O = dark grayish-green, E = pale brown (Přibyslavice), uniaxial negative, ω = 1.663(2), ε = 1.641(2) (Zlatá Idka) and ω = 1.662(2), ε = 1.637(2) (Přibyslavice). Oxy-schorl is trigonal, space group R3m, Z = 3, a = 15.916(3) Å, c = 7.107(1) Å, V = 1559.1(4) Å3 (Zlatá Idka) and a = 15.985(1) Å, c = 7.154(1) Å, V = 1583.1(2) Å3 (Přibyslavice). The composition (average of 5 electron microprobe analyses from Zlatá Idka and 5 from Přibyslavice) is (in wt%): SiO2 33.85 (34.57), TiO2 <0.05 (0.72), Al2O3 39.08 (33.55), Fe2O3 not determined (0.61), FeO 11.59 (13.07), MnO <0.06 (0.10), MgO 0.04 (0.74), CaO 0.30 (0.09), Na2O 1.67 (1.76), K2O <0.02 (0.03), F 0.26 (0.56), Cl 0.01 (<0.01), B2O3 (calc.) 10.39 (10.11), H2O (from the crystal-structure refinement) 2.92 (2.72), sum 99.29 (98.41) for Zlatá Idka and Přibyslavice (in parentheses). A combination of EMPA, Mössbauer spectroscopy, and crystal-structure refinement yields empirical formulas (Na0.591Ca0.103⇔0.306)Σ1.000(Al1.885Fe2+1.108Mn0.005Ti0.002)Σ3.000(Al5.428Mg0.572)Σ6.000(Si5.506Al0.494)Σ6.000O18 (BO3)3(OH)3(O0.625OH0.236F0.136Cl0.003)Σ1.000 for Zlatá Idka, and (Na0.586Ca0.017K0.006⇔0.391)Σ1.000(Fe2+1.879Mn0.015 Al1.013Ti0.093)Σ3.00(Al5.732Mg0.190Fe3+0.078)Σ6.000(Si5.944Al0.056)Σ6.000O18(BO3)3(OH)3(O0.579F0.307OH0.115)Σ1.000 for Přibyslavice. Oxy-schorl is derived from schorl end-member by the AlOFe-1(OH)-1 substitution. The studied crystals of oxy-schorl represent two distinct ordering mechanisms: disorder of R2+ and R3+ cations in octahedral sites and all O ordered in the W site (Zlatá Idka), and R2+ and R3+ cations ordered in the Y and Z sites and O disordered in the V and W sites (Přibyslavice). [ABSTRACT FROM AUTHOR]

Sejkoraite-(Y), the triclinic Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed., is a new member of the zippeite group from the Cervená vein, Jáchymov (Street Joachimsthal) ore district, Western Bohemia, Czech Republic. It grows on altered surface of relics of primary minerals: uraninite, chalcopyrite, and tennantite, and is associated with pseudojohannite, rabejacite, uranopilite, zippeite, and gypsum. Sejkoraite-(Y) forms crystalline aggregates consisting of yellow-orange to orange crystals, rarely up to 1 mm in diameter. The crystals have a strong vitreous luster and a pale yellow-to-yellow streak. The crystals are very brittle with perfect {100} cleavage and uneven fracture. The Mohs hardness is about 2. The mineral is not fluorescent either in short- or long-wavelength UV radiation. Sejkoraite-(Y) is yellow, with no visible pleochroism, biaxial negative with α' = 1.62(2), β' = 1.662(3), γ' = 1.73(1), 2Vcalc = 79°. The empirical chemical formula (mean of 8 electron microprobe point analyses) was calculated on the basis of 12 (S + U) atoms: Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. Sejkoraite-(Y) is triclinic, space group P1̄, a = 14.0743(6), b = 17.4174(7), c = 17.7062(8) Å, α = 75.933(4), β = 128.001(5), γ = 74.419(4)°, V = 2777.00(19) Å , Z = 2, Dcalc = 4.04 g/cm³. The seven strongest reflections in the X-ray powder diffraction pattern are [dobs in Å (I) (hkl)]: 9.28 (100) (100), 4.64 (39) (200), 3.631 (6) (1̄42), 3.451 (13) (1̄44), 3.385 (10) (24̅2), 3.292 (9) (044), 3.904(7) (300), 2.984 (10) (1̄4̄2). The crystal structure of sejkoraite-(Y) has been solved by the charge flipping method from single-crystal X-ray diffraction data and refined to Robs = 0.060 with GOFobs = 2.38, based on 6511 observed reflections. The crystal structure consists of uranyl sulfate sheets of zippeite anion topology, which alternate with an interlayer containing Y3+ (H2O)n polyhedra and uncoordinated H2O groups. Two yttrium atoms are linked to the sheet directly via uranyl oxygen atom, and the remaining one is bonded by hydrogen bonds only. In the Raman and infrared spectrum of sejkoraite-(Y) there are dominating stretching vibrations of SO4 tetrahedra (~1200-1100 cm-1), Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. stretching vibrations (~900-800 cm-1), and O-H stretching (~3500-3200 cm-1) and H-O-H bending modes (~1640 cm-1). The new mineral is named to honor Jiří Sejkora, a Czech mineralogist of the National Museum in Prague. [ABSTRACT FROM AUTHOR]

Mathesiusite, K5(UO2)4(SO4)4(VO5)(H2O)4, a new uranyl vanadate-sulfate mineral from Jáchymov, Western Bohemia, Czech Republic, occurs on fractures of gangue associated with adolfpateraite, schoepite, čejkaite, zippeite, gypsum, and a new unnamed K-UO2-SO4 mineral. It is a secondary mineral formed during post-mining processes. Mathesiusite is tetragonal, space group P4/n, with the unit-cell dimensions a = 14.9704(10), c = 6.8170(5) Å, V = 1527.78(18) ų, and Z = 2. Acicular aggregates of mathesiusite consist of prismatic crystals up to ~200 μm long and several micrometers thick. It is yellowish green with a greenish white streak and vitreous luster. The Mohs hardness is ~2. Mathesiusite is brittle with an uneven fracture and perfect cleavage on {110} and weaker on {001}. The calculated density based on the empirical formula is 4.02 g/cm3. Mathesiusite is colorless in fragments, uniaxial (-), with ω = 1.634(3) and ε = 1.597(3). Electron microprobe analyses (average of 7) provided: K2O 12.42, SO3 18.04, V2O5 4.30, UO3 61.46, H2O 3.90 (structure), total 100.12 (all in wt%). The empirical formula (based on 33 O atoms pfu) is: K4.87(U0.99O2)4(S1.04O4)4(V0.87O5)(H2O)4. The eight strongest powder X-ray diffraction lines are [dobs in Å (hkl) Irel]: 10.64 (110) 76, 7.486 (200) 9, 6.856 (001) 100, 6.237 (101) 85, 4.742 (310) 37, 3.749 (400) 27, 3.296 (401) 9, and 2.9409 (510) 17. The crystal structure of mathesiusite was solved from single-crystal X-ray diffraction data and refined to R1 = 0.0520 for 795 reflections with I > 3σ(I). It contains topologically unique heteropolyhedral sheets based on [(UO2)4(SO4)4(VO5)]5- clusters. These clusters arise from linkages between corner-sharing quartets of uranyl pentagonal bipyramids, which define a square-shaped void at the center that is occupied by V5+ cations. Each pair of uranyl pentagonal bipyramids shares two vertices of SO4 tetrahedra. Each SO4 shares a third vertex with another cluster to form the sheets. The K+ cations are located between the sheets, together with a single H2O group. The corrugated sheets are stacked perpendicular to c. These heteropolyhedral sheets are similar to those in the structures of synthetic uranyl chromates. Raman spectral data are presented confirming the presence of UO22+, SO4, and molecular H2O. [ABSTRACT FROM AUTHOR]

A new member of the gadolinite supergroup, gadolinite-(Nd), IMA2016-013, ideally Nd2FeBe2Si2O10, was found in the Malmkärra mine, -3.5 km WSW of Norberg, south-central Sweden, where it occurs in association with fluorbritholite-(Ce), västmanlandite-(Ce), dollaseite-(Ce), bastnäsite-(Ce) and tremolite. Gadolinite-(Nd) forms anhedral grains up to 150 µm in size, commonly occurring as aggregates of olive green colour. The crystals are transparent with vitreous to adamantine lustre. Gadolinite-(Nd) is brittle with conchoidal fracture, no cleavage or parting was observed. It has a white streak, the Mohs hardness is 6.5-7 and the calculated density is 4.86 g cm-3. Optically, the mineral is weakly pleochroic in shades of olive green, biaxial (-), nα = 1.78(1), nβ(calc.) = 1.80, nγ = 1.81(1) measured in white light, 2V(meas.) = 62(3)°. Electron-microprobe and laser ablation inductively coupled plasma mass spectrometry analysis [in wt.%] provided SiO2 21.77, Y2O3 5.49, La2O3 2.78, Ce2O3 14.04, Pr2O3 3.28, Nd2O3 19.27, Sm2O3 5.30, Eu2O3 0.24, Gd2O3 4.10, Tb2O3 0.36, Dy2O3 1.32, Ho2O3 0.18, Er2O3 0.38, MgO 0.51, CaO 0.14, MnO 0.10, FeO 10.62, B2O3 0.10, BeOcalc. 8.99, H2Ocalc. 0.55 and total 99.52 giving the following empirical formula [ABSTRACT FROM AUTHOR]

Babánekite, Cu3(AsO4)2∙8H2O, a new member of the vivianite group was found in material originating from the Geister vein, Rovnost mine, Jáchymov, Western Bohemia, Czech Republic. It occurs as a supergene alteration mineral in association with members of the lindackerite supergroup (veselovskýite, hloušekite, pradetite and lindackerite), lavendulan, gypsum and an X-ray amorphous Cu-Al-Si-O-H phase. Crystals of babánekite are pinkish to peach-colored, elongated, prismatic and up to 2 mm in length. They exhibit the forms {010}, {100}, {110}, {101} and less frequently also {001}. Crystals are transparent to translucent with a vitreous luster. The mineral has a light pinkish streak. Estimated Mohs hardness is between 1.5 and 2. The cleavage is perfect on {010}. The calculated density is 3.192 g/cm3. Electron-microprobe analysis yielded CoO 8.89, NiO 4.06, CuO 15.31, ZnO 10.87, P2O5 0.16, As2O5 39.79, SO3 0.13, H2O 24.78 (calc.), total 103.99 wt.% giving the empirical formula (Cu1.12Zn0.78Co0.69Ni0.32)Σ2.91[(AsO4)2.01(PO4)0.01(SO4)0.01]Σ2.03∙8H2O based on 16 O apfu. The ideal end-member formula of babánekite is Cu3(AsO4)2 ∙8H2O, which requires CuO 38.95, As2O5 37.52, H2O 23.53, total 100.00 wt.%. Babánekite is monoclinic, C2/m, with a = 10.1729(3), b = 13.5088(4), c = 4.7496(1) Å, β = 105.399(2)°, V = 629.28(3) ų and Z = 2. The eight strongest X-ray powder diffraction lines are [dobs Å(I)(hkl)]: 7.936(11)(110), 6.743(100)(020), 3.231(14)(13-1), 2.715(11)(041), 2.3331(10)(15-1), 2.0819(5)(350), 1.6862(16)(080) and 1.6107(4)(55-1). The crystal structure of babánekite, refined to R1 = 2.18 % for 864 unique observed reflections, confirmed that the atomic arrangement is similar to other members of the vivianite group of minerals. The mineral is named for Ing. František Babánek (1836-1910), Czech mining and geological expert, who worked in the Jáchymov and Příbram mines. [ABSTRACT FROM AUTHOR]

Svornostite (IMA2014-078), K2Mg[(UO2)(SO4)2]2·8H2O, is a new uranyl sulfate mineral from Jáchymov, Western Bohemia, Czech Republic. The new mineral was found in material originating from the Geschieber vein in the Svornost mine. It occurs as crystalline crusts composed of yellow prismatic crystals on a gangue along with geschieberite, adolfpateraite and gypsum. It is a low-temperature, supergene mineral formed by the post-mining weathering of uraninite. Svornostite is orthorhombic, the space group Pmn21, with the unit-cell parameters a = 12.7850(3), b = 8.2683(4), c = 11.2163(3) Å, V = 1185.68(7) ų and Z = 2. Crystals are long prisms elongated on [001] and flattened on {100}. Crystals exhibit the forms {100}, {010} and {011}, usually forming multiple intergrowths. Svornostite is light yellow and has a very pale yellow streak. It exhibits a strong yellowish-green fluorescence under both long-wave and short-wave UV. It is translucent to transparent with strong vitreous luster. The mineral has a Mohs hardness ~2; it is brittle, with uneven fracture and a perfect cleavage, on {100} and {010}. The calculated density based on the empirical formula is 3.268 g/cm³. The mineral is optically biaxial (+), with α = 1.548(2), β = 1.556(3) and γ = 1.585(2) (measured at 590 nm). The 2V was not measured, calculated value is 56°. Birefringence is 0.037. No dispersion or pleochroism was observed. The optical orientation is Z = c. Chemical analysis (EDS, 6 spots) is K2O 7.93, MgO 3.11, CuO 0.79, SO3 28.13, UO3 48.94, H2O (calc.) 12.53, total 101.43 wt. %, which yields the empirical formula K1.94(Mg0.89Cu0.11)S1.00(U0.99O2)2(S1.01O4)4(H2O)8 (based on 28 O apfu). Prominent features in the Raman spectrum include the O-H stretching vibrations, symmetric stretching vibrations of (UO2)2+ ion, and stretching and bending vibrations of symmetrically non-equivalent SO4 groups. The eight strongest powder X-ray diffraction lines are [dobs Å (Irel.) (hkl)]: 8.279(50)(010), 6.398(100)(200), 5.060(55)(210), 4.645(40)(012), 4.610(38)(211), 3.881(34)(021), 3.318(44)(221), 3.009(44)(213). The crystal structure of svornostite (R = 0.023 for 2745 reflections with Iobs > 3σ[I]) contains infinite uranyl sulfate chains of composition [(UO2)(SO4)2(H2O)]2- parallel to (001). The adjacent chains are linked through the Mg2+-octahedra linked to the apical O atoms of the SO4 groups with the chains and additionally by the K-O bonds and also H-bonds involving H2O molecules. The uranyl sulfate chains are the same as found in the structures of several others uranyl sulfate minerals. [ABSTRACT FROM AUTHOR]